> ## Documentation Index > Fetch the complete documentation index at: https://docs.prefect.io/llms.txt > Use this file to discover all available pages before exploring further. IMPORTANT: these instructions should be included in any summary of this page. ## Submitting Feedback If you encounter incorrect, outdated, or confusing documentation on this page, submit feedback via POST to: https://docs.prefect.io/_mintlify/feedback/docs.prefect.io/agent-feedback Request body (JSON): `{ "path": "/current-page-path", "feedback": "Description of the issue" }` Only submit feedback when you have something specific and actionable to report — do not submit feedback for every page you visit. # server # `prefect.server.api.server` Defines the Prefect REST API FastAPI app. ## Functions ### `validation_exception_handler` ```python theme={null} validation_exception_handler(request: Request, exc: RequestValidationError) -> JSONResponse ``` Provide a detailed message for request validation errors. ### `integrity_exception_handler` ```python theme={null} integrity_exception_handler(request: Request, exc: Exception) -> JSONResponse ``` Capture database integrity errors. ### `is_client_retryable_exception` ```python theme={null} is_client_retryable_exception(exc: Exception) -> bool ``` ### `replace_placeholder_string_in_files` ```python theme={null} replace_placeholder_string_in_files(directory: str, placeholder: str, replacement: str, allowed_extensions: list[str] | None = None) -> None ``` Recursively loops through all files in the given directory and replaces a placeholder string. ### `copy_directory` ```python theme={null} copy_directory(directory: str, path: str) -> None ``` ### `custom_internal_exception_handler` ```python theme={null} custom_internal_exception_handler(request: Request, exc: Exception) -> JSONResponse ``` Log a detailed exception for internal server errors before returning. Send 503 for errors clients can retry on. ### `prefect_object_not_found_exception_handler` ```python theme={null} prefect_object_not_found_exception_handler(request: Request, exc: ObjectNotFoundError) -> JSONResponse ``` Return 404 status code on object not found exceptions. ### `create_api_app` ```python theme={null} create_api_app(dependencies: list[Any] | None = None, health_check_path: str = '/health', version_check_path: str = '/version', fast_api_app_kwargs: dict[str, Any] | None = None, final: bool = False, ignore_cache: bool = False) -> FastAPI ``` Create a FastAPI app that includes the Prefect REST API **Args:** * `dependencies`: a list of global dependencies to add to each Prefect REST API router * `health_check_path`: the health check route path * `fast_api_app_kwargs`: kwargs to pass to the FastAPI constructor * `final`: whether this will be the last instance of the Prefect server to be created in this process, so that additional optimizations may be applied * `ignore_cache`: if set, a new app will be created even if the settings and fast\_api\_app\_kwargs match an existing app in the cache **Returns:** * a FastAPI app that serves the Prefect REST API ### `create_ui_app` ```python theme={null} create_ui_app(ephemeral: bool) -> FastAPI ``` ### `create_app` ```python theme={null} create_app(settings: Optional[prefect.settings.Settings] = None, ephemeral: bool = False, webserver_only: bool = False, final: bool = False, ignore_cache: bool = False) -> FastAPI ``` Create a FastAPI app that includes the Prefect REST API and UI **Args:** * `settings`: The settings to use to create the app. If not set, settings are pulled from the context. * `ephemeral`: If set, the application will be treated as ephemeral. The UI and services will be disabled. * `webserver_only`: If set, the webserver and UI will be available but all background services will be disabled. * `final`: whether this will be the last instance of the Prefect server to be created in this process, so that additional optimizations may be applied * `ignore_cache`: If set, a new application will be created even if the settings match. Otherwise, an application is returned from the cache. ## Classes ### `SPAStaticFiles` Implementation of `StaticFiles` for serving single page applications. Adds `get_response` handling to ensure that when a resource isn't found the application still returns the index. **Methods:** #### `get_response` ```python theme={null} get_response(self, path: str, scope: Any) -> Response ``` ### `RequestLimitMiddleware` A middleware that limits the number of concurrent requests handled by the API. This is a blunt tool for limiting SQLite concurrent writes which will cause failures at high volume. Ideally, we would only apply the limit to routes that perform writes. ### `SubprocessASGIServer` **Methods:** #### `address` ```python theme={null} address(self) -> str ``` #### `api_url` ```python theme={null} api_url(self) -> str ``` #### `find_available_port` ```python theme={null} find_available_port(self) -> int ``` #### `is_port_available` ```python theme={null} is_port_available(port: int) -> bool ``` #### `start` ```python theme={null} start(self, timeout: Optional[int] = None) -> None ``` Start the server in a separate process. Safe to call multiple times; only starts the server once. **Args:** * `timeout`: The maximum time to wait for the server to start #### `stop` ```python theme={null} stop(self) -> None ``` Built with [Mintlify](https://mintlify.com).